Adjustable support and alinement means for a multibeam infrared gas analyser



July 8, 1969 A. KOWERT ET AL 3,454,760 Y ADJUSTABLE SUPPORT' AND ALINEMENT MEANS FOR A MULTIBEAM Sheet I INFRARED GAS ANALYSER Filed Aug. 29, 1966 ADJUSTABLE SUPPORT AND ALINEMENT MEANS FOR A MULTIBEAM July 8 1969 owgm ET AL 3,454,760

INFRARED GAS ANALYSER Filed Aug. 29, 1966 Sheet 2 of 5 July 8, 1969 ow -r' ET AL 3,454,760

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ADJUSTABLE SUPPORT AND ALINEMENT MEANS FOR A MULTIBEAM INFR XRED GAS ANALYSER Filed Aug. 29, 1966 Sheet 5 of 5 United States Patent 3,454,760 ADJUSTABLE SUPPORT AND ALINEMENT MEANS FOR A MULTIBEAM INFRARED GAS ANALYSER Alexander Kowert, Gravenbruch Hesse, Kurt Moldenhauer, Frankfurt am Main, Ludwig Ries, Konigshofen (Taunus), and Werner Schaefer, Kelkheim-Munster, Germany, assignors to Hartmann & Braun Aktiengesellschaft, a corporation of Germany Filed Aug. 29, 1966, Ser. No. 575,733 Claims priority, application Germany, Sept. 1, 1965, H 57,045 Int. Cl. G01n 21/26 US. Cl. 250-435 17 Claims ABSTRACT OF THE DISCLOSURE A multibeam infrared analyser wherein a series of twin beam cell units are laid end-to-end in a trough with one end of the series abutting against a fixed twin radiator and a selectably slidable clamping detector in the trough abuts against the other end of the series to hold the series together in the trough. Means between the units as well as between the units and the radiator assure alinement. The trough and elements therein are housed for ready access and control of environment.

The invention relates to a multiple beam infrared gas analyser which operates by measuring the absorption of infrared rays by the gas that is to be analysed. More particularly the invention concerns the optical equipment contained in such apparatus.

One object of the invention is to provide a particularly economical arrangement of the components of the optical equipment.

Another object of the invention is to construct the individual components themselves in a particularly simple and compact way.

Yet another object of the invention is to dispose the components accessibly and in a manner occupying a minimum of space.

More generally speaking it is an object of the invention to combine and located the components conveniently and in a manner permitting each unit to be easily exchanged and replaced.

Finally, it is an object of the invention to contrive and construct the apparatus in a manner permitting accessory equipment needed for assuring a satisfactory and troublefree functioning of the optical equipment to be accommodated in the apparatus in the most useful way for achieving the desired effects and so that the accessory equipment can be of simple design and construction.

The components of the optical systems of infrared gas analysers known in the art normally comprise firstly a radiator unit which may contain one or more radiators for infrared radiation, preferably in the form of electrically heated wire filaments. Generally the radiator unit may also contain further optical aids, such as reflectors and shutters, for instance a motor-driven rotary segmental shutter for simultaneously or alternately interrupting the infrared beams. Secondly, gas cells which may consist of metal or glass, and which may have the form of elongated cylindrical vessels, will normally comprise analysing cells through which the gas that is to be tested can be conducted, reference cells containing a reference gas in the form of a gas of specific concentration that absorbs infrared rays or a gas that does not absorb and is inert to infrared rays, and filter cells which may likewise be interposed in the paths of the beams, and which contain a g that has a filtering effect on the rays and thereby permits the effects of unwanted components contained in the ana- 3,454,760 Patented July 8, 1969 lysed gas to be eliminated. The ends of the gas cells have windows that are transparent to infrared radiation. Finally, a detector unit in which the infrared radiation, having passed through the several cells wherein it has been partly absorbed, is converted into an electrical signal. The detector therefore contains devices which respond to incident infrared radiation, such as a so-called pneumatic receiver comprising two cells each filled with the tested gas 1' some alternative suitable gas and separated by a membrane which forms part of a capacitor in an electrical circuit. The pressure fluctuations inside the chambers due to absorption of the incident radiation are electrically measured by the change in capacity which they entrain, the measurement indicating the concentration of the tested gas. However, other types of radiation detectors may likewise be used, such as photoelectric devices that respond to infrared radiation or black radiation detectors based on the use of radiation-responsive thermocouples or bolometer devices. The signal generated by the detector is amplified in an output amplifier to provide a signal of sufficient strength to serve as the input signal of a following power amplifier. From the technical point of view it is advantageous to combine this output amplifier direct with the detector and thereby to reduce the length of the electrical leads between detector and amplifier for the elimination of any possible extraneous effects on the very sensitive amplifier arrangement. For performing the measurement the described components and parts of the gas analyser must be located in a particular sequence inside a housing and, as already mentioned, it is an object of the invention to permit this to be done conveniently and so that individual component units can be readily exchanged and replaced. Accessory equipment which it is desirable to provide includes for instance means for maintaining a constant temperature inside the housing containing the optical system and/or for preventing extraneous gases from affecting the infrared beams.

For achieving the objects that have been set forth above the multiple beam infrared gas analyser according to the present invention comprises optical equipment divided into a plurality of separate structural units, one unit containing a radiator with or without a rotary shutter, further units containing gas cells and a final unit containing radiation detectors with or without an output amplifier, said units being slidably mounted on a bench and having the form of cylindrical components of substantially like diameter through which the infrared beams pass parallel to the cylinder axis, whereas the bench is a member extending the full length of a housing containing the apparatus, and forming a trough adapted in cross section to receive the cylindrical components in coaxial alignment for location therein by clamping means.

This basic arrangement according to the invention is well adapted to be advantageously further developed with respect to the construction, disposition and location of the several components.

For instance, a particularly useful bench may be formed with a trough having an equilateral, upwardly open, prismatic cross section upon one end of which the radiator unit can be easily located by clamping means, such as one or more screws. A longitudinal slot may be provided in the floor of the prismatic trough for the insertion therethrough and the slidable longitudinal adjustment of clamping means for appropriately locating and affixing the cylindrical components to the bench.

Furthermore, the cylindrical components may be fitted together by providing them with appropriate adapters at their contiguous ends. Conveniently the interengaging parts of the adapters may be constituted by a machined annular socket or recess in one adapter and a matching hollow cylindrical member projecting from the cooperating adapter, recess and cylindrical member having a diameter smaller than that of the cylindrical components themselves. Moreover, one of each pair of cooperating adapters may be provided on its periphery with two holes, and the other provided at corresponding points of its periphery with two pins for insertion into said holes, the position of the pins and of the holes being slightly offset from the ends of a diameter to ensure that the two adapters will not fit together otherwise than in one particular peripheral position.

According to the invention the units containing the gas cells are hollow cylindrical components fitted at each end with an adapter containing circular openings with internal flanges for locating the ends of the gas cells in positions parallel to the cylinder axis, the gas cells being further held by an elastic insertion contained in an annular groove in the inside circumference nof the opeings in each of the adapters. The manner in which the cells are seated may be further improved by providing each of the two adapters of a gas cell unit with a central bore of which one is provided with threads, and by inserting an axially hollow screw with a cylindrical head lengthwise through the two bore ands screwing its end into the bore with the thread, the bore containing the cylindrical head of the bolt also containing a spring for resiliently pulling the adapters against the ends of the cylindrical gas cell component.

A particularly simple and effective form of construction comprises only one clamping means which locates the detector unit, the other units being located by the interengagement of their respective adapters. In such an arrangement it is preferred that the units interposed between the radiator unit and the detector unit should have a diameter that is slightly smaller than the diameter of the radiator and the detector unit, for instance by a fraction of a millimetre. This has the advantage that the component units and the bench need not be manufactured to extremely precise tolerations, since the components will automatically align themselves when they are assembled and fitted together on the bench.

For the performance of some measurements it may be useful if the interior of the optical equipment can be flushed with a gas that is inert to infrared radiation in order to prevent extraneous gases from entering the optical equipment and from interfering with the accuracy of the measurement. To this end the adapters formed with the machined recesses may be provided with lateral pipe connections communicating with the interior of said recesses, and for achieving a gastight connection between cooperating adapters an elastic sealing ring may be inserted between them.

Other features of the optical equipment of a multiple beam infrared gas analyser according to the invention relate to the accommodation of the equipment in a housing and to the necessary accessory means, particularly for the thermostatic control of the temperature inside the housing which is essential for making measurements of high precision.

So that the invention may be more readily understood an illustrative embodiment will be hereinafter more particularly described, by reference to the accompanying drawings. However, the following description is not intended to limit the scope of the invention as defined in the claims.

In the drawings:

FIG. 1 diagrammatically shows optical equipment disposed and constructed according to the invention, including accessory means for thermostatically controlling the temperature inside the housing of a twin-beam infrared gas analyser,

FIG. 2 is a perspective view showing the general external appearance of the optical equipment after this has been pulled out of its housing on a supporting tray,

FIG. 3 is a perspective view of a bench formed with a trough of prismatic cross section for mounting and locating the component units of the optical equipment,

FIG. 4 is an exploded view partly in axial section, of optical equipment according to the invention,

FIG. 5 is a view of the adapter fitted to the radiator component and illustrates the manner in which the adapters are provided with holes and corresponding pins for peripherally locating adjacent components, and

FIG. 6 is a fragmentary section of two cooperating adapters illustrating the manner in which the adapters interengage.

It will be understood from FIG. 1 that the optical equipment 2 of the exemplary twin-beam infrared gas analyser shown in the drawing comprises four units 2a, 2b, 2c and 2d. According to the invention these units have the form of cylindrical components of substantially like diameter through which the infrared beams pass parallel to the cylinder axis. The four components are mounted on a bench 4 which extends from one end to the other of a housing, and which is formed with a hollow trough of appropriate cross section for the reception and location therein by clamping means of the cylindrical components in coaxial alignment. It will be later described by reference to FIG. 4 that component 2a contains principally the radiators and a rotary shutter (radiator unit). The cylindrical components 2b and 2c contain gas cells (gas cell units), whereas the cylindrical component 2d contains the detector and an output amplifier (detector unit), the detector being accommodated in part 2:1 and the output amplifier in part 2d Attached to the outer face of the radiator unit is a motor 3 for driving the rotary shutter.

The bench 4 carrying the optical equipment is mounted on a tray 5 which is located roughly midway of the height of the housing 1, occupying the entire internal cross section of the housing which can be closed. The bench is mounted centrally on the tray 5 in such a way that the optical equipment is spaced the same distance away from the back of the housing as from the front which is formed by a removable cover not shown in the drawing. The tray can be withdrawn from the housing on two lateral slideways to provide all-round access to the optical equipment. Each slideway consists of an H-section rail 9 and two rail sections 8 which slidably embrace the two T-section halves of rail 9. One of the two rails 8 is directly secured to the tray, whereas the other is attached to an angle section 10 secured to the wall of the housing. The construction of this slideway is particularly clearly shown in FIG. 2. Furthermore, the housing 1 which is divided by the tray into an upper and a bottom compartment also contains inside the compartment under the tray the means required for the thermostatic temperature control of the optical system. For effecting control there are provided, directly under the radiator unit a radial flow fan 11, a heating resistor 12 located closely adjacent the air exit side of the fan and an adjustable thermostat 13 situated underneath the detector unit. As will be understood by also referring to FIG. 3 the fan draws air from the upper compartment of the housing through an opening 14 in the tray and two openings 15 in the sides of the bench, and propels this air, after deflection through over the heating resistor back again into the upper compartment through openings 16 at the other end of the tray on each side of the bench. The recirculation of the air inside the housing along a path which divides symmetrically on each side of the optical equipment permits an extremely uniform and constant temperature to be maintained inside the housing even when a thermostat is used which controls the heater in discontinuous steps.

Preferably the several units are mounted in a trough having an equilateral, upwardly open prismatic cross section and forming a bench as illustrated in FIG. 3. The radiator unit may be located at one end of the prismatic trough by screws. As already described the radiator unit rests in the prismatic trough above lateral openings 15 in the bench and a window 14 in the tray. If the radiator unit is provided with a socket for connecting electrical leads to the same and the leads are to enter from below, then the bottom of the bench may have another appropriate opening 18. The longitudinal slot 17 in the floor of the prism is intended for the reception of a bolt 6 afiixed to the detector unit as shown in section in FIG. 1. The threaded shaft of this belt also passes through a corresponding slot in the tray 5. When the gas cell units have been mounted in the prism the several units are slidably pushed together against the radiator unit and secured in position on the bench by tightening a wing nut 7 on the bolt.

The axial end faces of the several units are provided with adapters which engage when the optical units are assembled as has been described. The entire assembly is thus firmly located. Since only one clamping means is provided on the detector unit the optical equipment can be quickly and conveniently located even when cell units of varying lengths are employed. In lateral slots 61 of the bench further clamping means are provided for accessory equipment (FIG. 3). These clamping means 62 may be used for instance for securing gas supply pipes or in particular cases for holding additional stops which it may be desired to interpose in the path of the beams.

FIG. 4 illustrates the optical equipment in greater detail. The interengageable elements at the ends of each of the cylindrical components can be clearly seen. These have the form of shallow annular recesses or sockets 19 in one unit and of matching cylindrical extensions 20 on the cooperating unit. The radiator unit 2a contains the two radiation sources 21 and 22, each in the form of an electrically heatable Wire filament 23 and 24 respectively associated with reflectors 25, 26 for the projection of two parallel axial beams. The radiators are protected from the atmosphere inside the housing by windows 27, 28 made of a material that is transparent to infrared radiation, such as fluorite. A shutter 29 driven by the motor 3 rotates directly in front of these windows. This rotary shutter is arranged, according to the principle of measurement employed, to interrupt the two beams either simultaneously or in alternation.

The gas cell unit 2b which follows the radiator unit contains a measuring cell 30 and a reference cell 31. The gas that is to be examined enters the measuring cell through a pipe connection 32 and leaves through a second connection 33. The standardised construction of all the gas cell units will be exemplified by describing in detail the gas cell unit 2c which contains filtering cells 37, 38. By reference to the drawing it will be understood that a gas cell unit comprises a hollow cylinder 34 which at each end is fitted with an adapter 35 and 36 respectively for serial interfitting. The ends of the gas cells are inserted into recesses 39 machined into the insides of the adapters and are located by flanges 40. The infrared beams projected by the radiator units traverse the cylindrical gas cells axially, the cell axes being parallel to the principal axis of the cylinder unit of the optical equipment in which they are contained. The end faces of the gas cells are therefore made of a material that is transparent to infrared radiation. In order to protect the cells which may otherwise be made of glass as well as the fragile cell windows an internal peripheral groove 41 is machined into each of the adapters and contains an elastic insertion 42 for safely holding the cells. Moreover, in the axial direction the cells are cushioned in relation to the adapters. To this end the adapters are each formed with a central bore of which one is provided with threads 44, whereas the other contains a coiled spring 46. A hollow shafted screw 45 with a cylindrical head is inserted and screwed into the bores. The compressed coil spring then operates to retain the cells resiliently in the axial direction. The hollow outer cylinders incidentally have a temperature regulating effect inasmuch as their presence diminishes the effect of any possible temperature fluctuations on the gas cells. The detector unit 2d contains two chambers 47 and 48, each closed by a window 49 and 50 which forms a gas-tight seal, and which is transparent to infrared radiation. Each chamber is filled with a gas which responds to infrared radiation. Absorption by the gas of the infrared beams causes dilferen'tial gas pressures to arise in the cells containing the tested gas and a reference gas. Owing to the rotation of the rotary shutter these pressures cyclically fluctuate. Through ducts 51 and 52 the pressures are applied to opposite sides of an elastic membrane 53 which forms part of a capacitor device 54 functioning as a transducer to convert the pressure fluctuations into an electrical signal.

Correct peripheral alignment of the cells between the radiator unit and the detector unit in the path of the beams is assured by locating means on the adapters. These locating means have the form of holes drilled axailly into the circumference of one adapter and corresponding pins projecting from the cooperating circumference of the other adapter. FIG. 5 is an axial view of the radiator unit showing the rotary shutter 29 and the radiator openings. It will be seen that the adapter of the radiator unit may have two holes 58 and 59 on its circumference for the reception of corresponding pins on the circumference of the adapter of the adjacent gas cell unit. The units are assembled by rotating the gas cell unit until the pins align with and can be pushed into the holes, as indicated in FIG. 6. Preferably the holes and pins are not exactly diametrically opposite but situated at a relative angle which slightly differs from 180". The two parts will then fit together in only one particular circumferential position.

It may be desirable for the units in FIG. 4 to fit together in a gas-tight manner. Extraneous gas is thus prevented from entering the optical equipment and from introducing an error into the measurement. For this purpose sealing rings may be interposed between contiguous units. A particularly effective method of preventing extraneous gases from interfering with the beams consists in passing a suitable flushing gas through the optical equipment by making use of pipe connections 56 and 57. More particularly, flushing may be continuous since the cylinder headed screws 45 in the gas cell units are axially hollow and provide communication between the cavities in the gas cell unit assembly. The flushing gas may thus be admitted through connection 56 and exhausted through the other pipe connection 57.

It will be understood that the invention is not intended to be limited in scope to the particular embodiment that has been described which could be modified in various respects. For instance, for the application of a diiferent principle of measurement more than two beams and the necessary additional equipment could be provided. Numerous modifications of the described arrangement are also possible, more particularly with reference to the nature and construction of the radiators and the radiation detector. Some of the parts that have been described may also be lacking. For example, the above described pneumatic detector could be replaced by a photo-electric or a thermo-electric detector or the rotary shutter and its driv ing motor might be dispensed with if a continuous beam instead of an intermittent beam is to be used.

What is claimed is:

1. A multiple beam infrared gas analyser comprising a housing containing optical equipment in the form of a plurality of separate cylindrical units of approximately like diameter of which one is a radiator unit for the generation of parallel infrared beams, whereas further units are gas cell units containing gas cells and one unit is a detector unit responsive to said infrared beams, and a bench providing a trough of prismatic cross section upon one end of which the radiator unit is fixedly mounted, whereas said gas cell units and finally said detector unit are insertable into said trough in consecutive axial alignment and slidable therein into contact with said radiator unit and with each other and thus locatable by clamping means insertable through a slot in the base of said trough for engaging, locating and fixing said detector unit in said trough.

2. An analyzer as claimed in claim 1 said clamping means being a bolt fast on the detector unit and having a wing nut engaging on the base at the margins of the slot.

3. An analyzer as claimed in claim 1 and resilient gas sealing means between the units.

4. A multiple beam infrared gas analyzer comprising a housing containing optical equipment in the form of a plurality of separate cylindrical units of like diameter mounted on a trough section bench in coaxial contiguous alignment, and interengageable substantailly ring-shaped adapters affixed to the abutting axial ends of each of said units, one of each cooperating pair of said adapters being provided on its periphery with two holes at points offset from the ends of a diameter of said ring-shaped adapters, whereas the other is provided at corresponding points of its periphery with two pins insertable into said holes so that said cylindrical units can be fitted together in said coaxial contiguous alignment in only one particular relative position of their peripheries about their cylinder axes.

5. A multiple beam infrared gas analyser comprising a housing containing optical equipment in the form of a plurality of separate cylindrical units of which one is a radiator unit for generating parallel infrared beams whereas others are gas cell units and a final unit is a detector unit for infrared radiation, all said units being mounted on a trough section bench in coaxial contiguous alignment and relatively locatable by interengaging adapters afiixed to the abutting ends of said units, the adapters at the two ends of each of said gas cell units being provided with circular openings with internal flanges for the reception of the ends of gas cells in positions parallel to the axis of said gas cell unit and said gas cells being further held by elastic insertions contained in annular grooves in the inner circumference of said openings.

6. A multiple beam infrared gas analyser as set forth in claim 5, wherein said adapters at the ends of the gas cell units each have a central bore of which one is provided with threads, a hollow shafted screw with a cylindrical head being insertable lengthwise through said cylindrical gas cell unit by being passed through said bores and screwed into said threaded bore, whereas, a spring is provided in the other of said bores which receives the cylindrical head of said screw for pulling said adapters at the ends of the gas cell units resiliently together against the ends of said gas cells.

7. A multiple beam infrared gas analyser as set forth in claim 5, wherein the diameter of the cylindrical gas cell units is a fraction of a millimetre less than the diameters of said radiator unit and said detector unit, which are both equal.

8. A multiple beam infrared gas analyser comprising a housing, optical equipment in the form of a plurality of separate cylindrical units of which one is a radiator unit for the generation of parallel infrared beams, whereas others are gas cell units containing gas cells for the gas that is to be analysed, a reference gas and gases for filtering the infrared beams and a final unit contains detection equipment responsive to infrared rays and adapted to generate an electrical signal that can be measured, interengaging adapters fitted to said units for relatively locating said units in contiguous axial and appropriate circumferential alignment on a trough section bench in said housing, cooperating pairs of said adapters being provided on the one hand with an annular socket and on the other hand with a hollow cylindrical extension that fits into said socket, and means for flushing out said optical equipment with a gas that is unresponsive to infrared rays,

said means consisting of pipe connections on said adapters which contain said annular sockets, said pipe connections communicating with the interior of said annular sockets.

9. A multiple beam infrared gas analyser as set forth in claim 8, wherein a sealing ring is interposed between each pair of contiguous units;

10. A multiple beam infrared gas analyser as set forth in claim 8, wherein the trough of said bench has a prismatic cross section and said bench is provided externally with longitudinal slots for the slidable reception of clamping means for holding gas admission and like pipes as well as stops required to be inserted into the path of the infrared beams.

11. A multiple beam'infrared gas analyser, as set forth in claim 8, wherein said bench is centrally mounted on a horizontal tray slidably withdrawable from the interior of said housing on rails affixed at a level halfway up the sides of said housing which can be closed when said tray has been pushed inwardly on said rails substantially into said housing.

12. A multiple beam infrared gas analyser, as set forth in claim 11, wherein said tray extends across the entire internal cross section of said housing dividing the same into an upper and a lower compartment, and a fan is accommodated in said lower compartment for circulating air through both said compartments, openings for the passage therethrough of the air being provided in the ends of said tray and in corresponding positions in said bench.

13. A multiple beam infrared analyser, as set forth in claim 12, comprising a supplementary heating element controlled by an adjustable thermostat inside said lower compartment, adapted to maintain said circulating air at a desired constant temperature level.

14. A multiple beam infrared gas analyser comprising a elongated mounting bench of generally trough shape having an upwardly open slot longitudinal of the bench and wider toward the top than toward the bottom giving the transverse cross-section of the space of the slot the shape of a wedge, a plurality of adjacent cylindrical analyser units of nearly like diameter abutting one another at at least one end of the respective units and all substantially in axial alignment on the bench, one of said units being a radiator unit fixedly mounted on the bench, another of said units being a detector unit at least partially lying in the slot and at least one of the units being a gas cell unit at least partially lying in the slot and between the radiator and detector units, the abutting ends of the units having round sockets and mating projections in the axial direction of the units at the respective ends, the bench having a base portion below said slot and provided with an elongated opening therethrough, and adjustable clamping means on the detector unit insertable through said opening for clamping only the detector unit substantially rigidly with respect to the bench.

15. An analyser as claimed in claim 14, said opening being substantially parallel with the axes of the units to permit movement of the means within the opening in the axial direction of the units to enable urging of the units together before the clamping means clamps the detector unit on the bench.

16. An analyzer as claimed in claim 14, the cross section of the space of the slot being substantially constant and over the base where it receives the detector and gas cell units, and the gas cell unit being of slightly less diameter than the radiator and detector units to insure that the gas cell unit may be laid in the slot and aligned between the radiator and detector units.

17. An analyser as claimed in claim 14, the gas cell units and the detector unit being selectively slidable in the slot for bringing all of said units into their abutment before clamping of the detector unit.

(References on following page) References Cited UNITED STATES PATENTS A. L. BIRCH, Assistant Examiner.

12/1954 Skarstrom 250-435 12/1958 Willis 2s0 43.s CL 12/1960 Smart 2s0 43.s 5 35651, 201

2/1961 Waters et a1 250-435 RALPH G. NILSON, Primary Examiner. 

